This invention is a new aquatic body propulsion device or swim fin for attachment to the human foot. It is designed for swimmers and swim fin users involved in various surface and underwater swimming sports. Such sports include recreational swimming, competitive swimming, surfing, body-surfing, kick-boarding, body-boarding, knee-boarding, free-diving, snorkeling, skin-diving, scuba-diving and the like.
This new fin is ergonomically designed to take advantage of the natural movements of the torso, legs and feet commonly found in the flutter kick. This enables improved hydrodynamics, propulsion and efficiency. To effectively illustrate the advantages of this new swim fin, the critical yet often overlooked aspects of the flutter kick will be described.
The flutter kick is fundamentally an alternating oscillation involving the legs and feet with a definitive up-stroke and down-stroke. The primary purpose of each sequential "whip-like" stroke is to effectively and efficiently push against the water. This in turn causes a reactive forward propulsion of the body through the water.
Many experts recognize the flutter kick as a crucial counteraction to stabilize the upper torso during the crawl stroke. This kick may involve a sequence of flexion, extension and rotation of various joints from the lumbar vertebrae of the lower back to the flanges of the toes. The specific position of the lower foot for accelerating into the whipping sequence determines the effectiveness and quantity of force generated. The foot position desired is one which provides the widest and flattest surface possible for pushing potential.
The primary movements involved in the flutter kick are anatomical flexion and extension of the hips, knees and ankles. However, many swimmers display styles that incorporate body rotation, hip rotation and medial femoral (upper leg) rotation. Of substantial concern is the ankle and foot undergo motion in a horizontal and oblique plane as well as in the vertical plane. This horizontal movement is limited to inward or medial rotation and commonly referred to as pigeon-toeing, toeing-in or turning-in. The anatomical term is supination, which is defined as inversion and adduction of the ankle and tarsel joints of the foot.
Supination or toeing-in results from the anatomical structure of the ankle and foot. Also, the water pressure against the foot's surface, the relaxation of appropriate muscles and the conscious awareness of the optimal foot position contributes to supination. Swimmers possessing a naturally propelling flutter kick display varying degrees of supination both in the up-stroke and the down-stroke.
During the down-stroke the foot supinates naturally in order to contact more water with the top of the foot. This in turn pushes the water backwards at a more effective angle, as the foot can be extended further in this position. In many cases hyperextension of the lower foot is achieved through supination, thereby adding more pushing power in the downward stroke.
When the anatomical centerline of the foot has angled inwardly during supination, the alignment of the toes changes in reference to the direction of travel of the swimmer. This toe line which can be 65.degree. offset from the anatomical line of the foot, can increase to an approximate 90.degree. angle, perpendicular to the direction of travel.
During the upstroke the foot rotates laterally but stops short of anatomical alignment, thus retaining a degree of supination. Importantly, it should be noted that the angle of supination in both the upward and downward stroke relates directly to the speed and force of the flutter kick. Test results show that the more vigorous the kick the greater the degree of natural supination.
This toe-in or supinated position is observed in the flutter kick of both the crawl stroke (when the swimmer is ventral side down) and the back stroke (when the swimmer is ventral side up). The foot moves into supination only during the leg stroke that moves the foot towards the ventral side of the swimmer. The foot moves away from supination and back towards anatomical alignment during the leg stroke that moves the foot toward the dorsal or back side of the swimmer. Therefore, since the terms upstroke and downstroke can become confusing when speaking of the crawl and back strokes, we will now use the terms ventral and dorsal when examining the flutter kick motion.
Once again defined as inversion and adduction of the lower foot, supination, as applied to a swimmer's foot motion, is somewhat different than foot supination in a standing or weight bearing position. In the flutter kick, a strong emphasis is placed on inversion of the foot and less emphasis on adduction. However, since similar foot muscles control both positions, a significant degree of adduction is usually present. This can be undesirable because it angles or pitches the foot into a position less than optimal for propulsion.
Swimmers with substantial adduction in their supinated foot position, will inwardly rotate the femor or thigh to an appropriate degree that tilts the foot back into a position for optimal push against the water.
Now therefore, there are three significant foot occurrences which compose a Kenetically Improved Kicking position in the ventral kick. They are: (1) foot supination; (2) an adjusting and proportionate degree of inward femoral rotation; and (3) foot extension. In the dorsal kick therefore the foot and leg return back to anatomical alignment.
The aforementioned anatomical movements involved in the flutter kick are in general observed and practiced by proficient and competitive participants in the field of swimming and finswimming disciplines. disciplines.
This complete motion of the ventral and dorsal kick can be termed the Kinetically Improved Kicking Cycle or the KIK Cycle. A specific definition of the KIK Cycle is as follows: The complete flutter kick cycle of a leg, including the ventral and dorsal kicks, whereby the foot undergoes changes in position which optimize its alignment for push against the water.
The KIK Cycle will vary among swimmers depending upon foot and ankle flexability, swimming style and experience. This invention specifically addresses supination and the KIK cycle by adapting to and allowing for these natural movements, while increasing performance and comfort.